This invention relates generally to numerically controlled machine tools having an automatic tool changer thereon and, more specifically, to a numerically controlled automatic tool changing machining center having a bar-type spindle.
In the past, machine tools have been constructed with automatic tool changers capable of accommodating either single shank toolholders or large multiple spindle toolheads weighing as much as 500 kgs. (1,000 lbs.) but not both. Machine tools having automatic tool changers thereon capable of exchanging single shank toolholders are usually fabricated with the tool storage magazine mounted on either the machine tool column or on the machine tool spindlehead. Such an arrangement precludes accommodation of large multiple spindle toolheads since the storage of one or more heavy multiple spindle toolheads in a spindlehead-mounted or column-mounted tool storage magazine will likely place an undue strain on the upright, tending to adversely affect machine tool accuracy. On the other hand, machine tool automatic tool changers which are designed to exchange large multiple spindle toolheads are typically unable, because of the large size and bulk of the tool changer mechanism, to accommodate smaller single shank toolholders.
In an attempt to overcome this difficulty, the machine tool and automatic tool changer therefore described and claimed in U.S. Pat. No. 4,288,909 issued on Sept. 15, 1981 was invented. The automatic tool changer described and claimed in this patent comprises a tool storage magazine, which, together with the machine tool upright, is mounted on a saddle that is slidably mounted on the machine tool bed so that the upright and machine tool column move in unison. The upright slidably supports a spindlehead in which is rotatably journaled a spindle for carrying a selected one of the multiple spindle toolheads and single toolholders which are vertically stored in the tool storage magazine. To accomplish a tool exchange, a toolholder or multiple spindle toolhead stored in the tool storage magazine is transferred from the tool storage magazine by a first tool gripper to a tilt unit which tilts the tool 90.degree. to enable a double ended tool changer arm mounted on the saddle to exchange the tool held in the tilt unit with the tool then engaged in the spindle. A multiple spindle toolhead transferred from the tool storage magazine to the spindle in this manner is secured to the spindlehead by a breach lock mechanism comprised of a plurality of threaded studs each extending rearwardly from the toolhead into a complementary threaded collar in the machine tool spindlehead adjacent to the spindle. Each threaded collar is rotatably driven by a ball screw to engage its complementary stud on the toolhead so as to urge the toolhead against the spindle.
While the above-described machine tool is capable of accommodating both single toolholders and multiple spindle toolheads, thus overcoming the disadvantages of the aforementioned prior art automatic tool changers, the previously invented automatic tool changer necessitates a relatively complicated breach lock arrangement for securing multiple spindle toolheads against the machine tool to prevent rotation of the toolhead body when the toolhead input shank is driven by the spindle. In contrast, my present invention concerns an automatic tool changing machining center whose spindle has a bar concentric therein for extension from the spindle to engage a toolholder or multiple spindle toolhead. The bar is retractable into the spindle for urging a large single toolholder, when so engaged by the spindle bar, against the spindle nose and for urging a multiple spindle toolhead, when so engaged by the spindle bar against the machine tool so that locating pins extending rearwardly from the multiple spindle toolhead body engage complementary locating cones secured on the machine tool thereby securing the multiple spindle toolhead body against rotation.